Modularise handlers.

src/js/plugin/handler/native-scroll.js

@@ -0,0 +1,18 @@
+/* Copyright (c) 2015 Hyunje Alex Jun and other contributors
+ * Licensed under the MIT License
+ */
+'use strict';
+
+var instances = require('../instances')
+  , updateGeometry = require('../update');
+
+function bindNativeScrollHandler(element, i) {
+  i.event.bind(element, 'scroll', function () {
+    updateGeometry(element);
+  });
+}
+
+module.exports = function (element) {
+  var i = instances.get(element);
+  bindNativeScrollHandler(element, i);
+};